System for stabilizing the spine and reducing spondylolisthesis

ABSTRACT

A system for achieving reduction of curvature of the lumbar region of the spine associated with spondylolisthesis includes transverse plates affixed to vertebrae L4 and L5 and sacral plates affixed to opposite sides of the sacrum. These plates in combination with the longitudinal plate along the posterior anterior plane in which the spinous processes lie allows for effective reduction of the curvature and secure fixation of this region of the spine. The transverse plates include textured surfaces which allow them to mate in a manner which prevents undesirable slippage therebetween. The system is also compact and does not interfere with the paraspinal muscles which run along either side of the spinous processes.

This application is a division of application Ser. No. 08/339,580, filedNov. 14, 1994, still pending, which is a continuation of applicationSer. No. 08/031,374, filed Mar. 11, 1993, now abandoned.

FIELD OF THE INVENTION

The present invention relates to surgical devices and methods forreducing deformity of the spine, and particularly the lumbar, andholding the spine while a spine fusion heals. While the invention iscapable of reducing mild rotational deformity, it particularly relatesto the reduction of spondylolisthesis.

BACKGROUND OF THE INVENTION

Spondylolisthesis is a condition of the spine where one vertebraesegment moves forward abnormally both in flexion (rotation) andtranslation relative to the vertebra immediately below it. This may bedue to (a) torn soft tissue restraints (ligaments, joint capsules,etc.), (b) eroded and deformed joints (degenerating spondylolisthesis),or (c) a defect in the bone between the lamina, spinal process andtransverse process as one unit and the rest of the vertebrae as a secondunit (spondylolytic spondylolisthesis).

When spondylolisthesis is present, the upper vertebral segment movesanteriorly in a saggital plane both in an angular flexion, as well as astraight translational direction. Generally, treatment ofspondylolisthesis corrects both types of displacement so that theflexion and translation of the upper element and the relative extensionof translation of the lower element are both corrected to restore thenormal lordotic alignment of the lumbar spine.

One way to treat spondylolisthesis is to reduce the deformity with apair of longitudinal plates attached at each level S-1, L-5 and L-4 bymeans of pedicle screws, (e.g., Roy Camille plates or variable slottedplates (Steppe plates.) Since the pedicle screws are angled medially inline with the long axis of the pedicle, the distance between the tips ofthe screws and the position where the screw will ultimately attach tothe plate is different. Another difficulty with longitudinal plates isaligning multiple screws inserted at different pedicle angles even if noreduction is performed. A third problem is that reducing using onlylongitudinal plates is much weaker than reducing with two pedicle screwspre-connected with a transverse connecting plate. Longitudinal platesalso place a large mass of metal over the facet joints where theyrestrict the ingrowth of blood vessels into the healing fusion and thusinhibit bone formation. The mass of the plates and screw attachment isalso in the middle of the paraspinal muscles (instead of between themuscles) creating more dead space and scar tissue.

It is desirable to have a system for treating spondylolisthesis thatprovides secure fixation of the lower lumbar region of the spine andeffectively reduces the accentuated curvature resulting fromspondylolisthesis. Such desirable system would also include a platedesign that does not interfere with the paraspinal muscles. Furthermore,it would be desirable if the system would allow for adjustment of thepositional relationship between the plates and the pedicle screws sothat optimum plate placement could be maintained before, during, andafter reduction.

SUMMARY OF THE INVENTION

The present invention relates to a system and the components of such asystem for stabilizing the lower lumbar region of the spine and forreducing displacement of vertebrae L4, L5, and the sacrum resulting fromthe condition known as spondylolisthesis. The system includesinstrumentation that achieves the above objectives without interferingwith the paraspinal muscles and permits one to maintain an optimum plateposition before, during and after reduction.

The system formed in accordance with the present invention includesfirst and second transverse plates for securing to vertebrae L4, andthird and fourth transverse plates for securing to vertebrae L5. Thefirst, second, third, and fourth transverse plates each include at oneend a bore for receiving a pedicle screw along a first axis. Extendingfrom the bore in a direction transverse to the first axis are twosubstantially parallel spaced-apart fingers of substantially equallength. Each pair of spaced-apart fingers include a superior surface andan opposing inferior surface. The inferior surfaces of the spaced-apartfingers of the first and third transverse plates are textured and thesuperior surfaces of the spaced-apart fingers of the second and fourthtransverse plates are textured. The system also includes first andsecond sacral plates that include a substantially planar body carrying aplurality of bores for rigidly fixing the sacral plates independently toopposite lateral portions of a sacrum. Extending from the body of eachsacral plate are two substantially parallel spaced-apart fingers ofsubstantially equal length having superior and opposing inferiorsurface. The inferior surfaces of the spaced-apart fingers of the firstsacral plate are textured and the superior surfaces of the spaced-apartfingers of the second sacral plate am textured. A longitudinal memberthat includes a superior end and an inferior end connected by elongatespaced-apart members is also part of the system. The superior end,inferior end, and the spaced-apart members define a slot in thelongitudinal plate. The longitudinal plate, transverse plates, andsacral plates are secured together by fasteners. The fasteners securethe spaced-apart fingers of the transverse plates and the sacral platesto the longitudinal plate.

The present invention also relates to the individual transverse platesand sacral plates that are components of the system described above.With respect to the transverse plates, either the inferior surface ofthe spaced-apart fingers or the superior surface of the spaced-apartfingers are textured with a repetitive pattern having an amplituderanging from about 15 to about 25 thousandths of an inch. Additionally,with the transverse plates, the spaced-apart fingers may be aligned withor offset from the first axis of the bore in accordance with the presentinvention. With respect to the sacral plates, as with the transverseplates, either the inferior or superior surface of the spaced-apartfingers are textured with a repetitive pattern having an amplituderanging from about 15 to about 25 thousandths of an inch.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is an elevational view of the left side of vertebrae L4, L5 andthe sacrum with portions of the same being cut away;

FIG. 2 is an elevational view of the posterior of the lumbar region ofthe spine with the system formed in accordance with the presentinvention applied thereto;

FIG. 3 is an exploded perspective view of the components of the systemformed in accordance with the present invention;

FIG. 4 is a plan view in the inferior direction of vertebrae L5 alongline 4--4 in FIG. 2; and

FIG. 5 is a plan view in the inferior direction of the sacrum along line5--5 in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the ghost line depiction in FIG. 1, spondylolisthesis is acondition of the lumbar region of spine 10 wherein the spinous process,lamina, and inferior articular processes of the fifth lumbar vertebrae(and sometimes the fourth lumbar vertebrae) are united together, butseparate from the rest of the bone. This condition results in anaccentuated curvature in an anterior direction (indicated by arrow 12)of the lumbar region of the spine and displacement of the sacrum in aposterior direction (indicated by arrow 16). As described above,correction of this curvature is achieved by pushing sacrum 14 in theanterior direction and pulling on vertebrae L4 and L5 in posteriordirection 16.

Referring additionally to FIG. 2, the system formed in accordance withthe present invention for fixating the lumbar region of a spine 10 andreducing spondylolisthesis includes first transverse plate 22 and secondtransverse plate 24 that are respectively attached to left pedicle 26and right pedicle 28 of vertebrae L4 with respective pedicle screws 30and 31. Third transverse plate 32 and fourth transverse plate 34 arerespectively attached to left pedicle 36 and right pedicle 38 ofvertebrae L5 with respective pedicle screws 40 and 41. The system alsoincludes, first sacral plate 42 and second sacral plate 44 that areattached to sacrum 14 adjacent the lumbosacral junction on oppositelateral sides thereof. Positioned along an axis transverse to transverseplates 22, 24, 32, and 34 and sacral plates 42 and 44 is longitudinalplate 46 that is concave in the posterior direction to allow forfixation of the lower lumbar region of spine 10 in the desired position.Transverse plates 22, 24, 32, and 34 and sacral plates 42 and 44 areconnected to longitudinal plate 46 by fasteners 48, 50, and 52 that aredescribed below in more detail.

Referring specifically to FIG. 3, the individual components making upthe system generally described above are illustrated in more detail anddescribed below. First transverse plate 22 includes a bore 54 at leftend 56. Left end 56 is rounded and bore 54 is centered therein and issized to receive pedicle screw 30 along a first axis. Pedicle screw 30includes a primary threaded portion 5 at one end for insertion into nut62 and a secondary threaded portion 60 at the opposite end for receivingpedicle nut 26 which secures pedicle screw 30 to first transverse plate22. Extending in the inferior direction 63 from left end 56 isrectangular flange 64. Flange 64 provides an offset element from whichelongate spaced-apart fingers 66 extend in a lateral directionsubstantially transverse to the first axis. Spaced-apart fingers 66 aresubstantially equal in length and include ends opposite flange 64 thatare connected by transverse end member 68. In this manner, flange 64,spaced-apart fingers 66, and end member 68 define a slot 70 that passesthrough first transverse plate 22. Flange 64 is also canted laterallyfrom right to left in the anterior direction 12 so that the plane inwhich left end 56 and flange 64 lie is different from the plane in whichspaced-apart fingers 66 and end member 68 lie.

Left end 56 and range64 have a thickness D measured from posteriorsurface 72 to anterior surface 74. Spaced-apart fingers 66 and endmember 68 have a thickness measured from posterior surface 72 andanterior surface 74 equal to about one-half D. In order to provide thenarrow thickness of spaced-apart fingers 66 and end member 68, a portionof anterior surface 74 is removed. For first transverse plate 22,anterior surface 74 of spaced-apart fingers 66 and end member 68 aretextured with serrations. The peaks and valleys of the serrations have arepetitive pattern having an amplitude of approximately 15 to 25thousandths of an inch. Other repetitive patterns can be used providedthey help to prevent slippage between first transverse plate 22 andsecond transverse plate 24 as described below in more detail. In theillustrated embodiment, first transverse plate 22 has been illustratedwith an offset provided by flange 64. Alternatively, first transverseplate 24 can be straight like the third and fourth transverse platesdescribed below in more detail.

Continuing to refer primarily to FIG. 3, second transverse plate 24 forvertebrae L4 includes right end 76 that includes bore 78 and flange 80that are substantially mirror images of left end 56, bore 54, and flange64 of first transverse plate 22. Accordingly, these features will not bedescribed in any more detail. Second transverse plate 24 differs fromfirst transverse plate 22 in that spaced-apart fingers 82 and transverseend member 84 include posterior surface 86 and anterior surface 88,wherein posterior surface 86 is textured as described above. In order toprovide the narrowed thickness of spaced-apart fingers 82 and end member84, a portion of posterior surface 86 is removed. When texturedposterior surface 86 of spaced-apart fingers 82 and end member 84 ofsecond transverse plate 24 and textured anterior surface 74 ofspaced-apart fingers 66 and end member 68 of first transverse plate 22are mated together, slippage therebetween is minimized because of themating of the textured surfaces.

Continuing to refer primarily to FIG. 3, third transverse plate 32includes a left end 90 that is a substantially circular plate andincludes bore 92 passing perpendicularly therethrough for receivingpedicle screw 40 along a first axis. Pedicle screw 40 is identical topedicle screw 30 described above. Extending from left end 90 aresubstantially parallel spaced-apart fingers 94 of substantially equallength. Ends of spaced-apart fingers 94 opposite left end 90 areconnected by transverse end member 96. Left end 90 is canted laterallyfrom right to left in an anterior direction so that left end 90 lies ina plane different from a plane in which spaced-apart fingers 94 and endmember 96 lie. Left end 90, spaced-apart fingers 94 and end member 96define a slot 98 passing through third transverse plate 32. Spaced-apartfingers 94 and end member 96 have a thickness in the posterior toanterior direction approximately equal to one-half the thickness of leftend 90 in the same direction. Spaced-apart fingers 94 and end member 96include posterior surface 100 and an opposing anterior surface 102. Thereduced thickness of spaced-apart fingers 94 and end member 96 isprovided by removing a portion of anterior surface 102. As describedabove with respect to first transverse plate 22, inferior surface 102 istextured.

Continuing to refer to FIG. 3, fourth transverse plate 34 includes rightend 104, that is substantially a mirror image of left end 90 of thirdtransverse plate 32. Right end 104 includes bore 106 that passes throughright end 104. Similar to left end 90 of third transverse plate 32,right end 104 is canted laterally from left to right in an anteriordirection 12. Fourth transverse plate 34 also includes substantiallyparallel spaced-apart fingers 108 that extend laterally from right end104. Spacedapart fingers 108 are substantially equal in length and areconnected at an end opposite right end 104 by transverse end member 110.Right end 104, spaced-apart fingers 108, and end member 110 define slot112 passing through fourth transverse plate 34. As with third transverseplate 32, spaced-apart fingers 108 and end member 110 have a thicknessin the posterior to anterior direction that is approximately equal toone-half the thickness of right end 104 in the same direction. Thisreduced thickness is provided by removing a portion of posterior surface114 of spaced-apart fingers 108 and end member 110. Fourth transverseplate 34 includes spaced-apart fingers 108 whose posterior 114 istextured with the repetitive pattern described above with respect to theother transverse plates. The repetitive pattern of fourth transverseplate 34 will mate up with the repetitive third transverse plate 32 toprevent slippage therebetween.

As noted above, it should be understood that while first and secondtransverse plates 22 and 24 described above and illustrated in FIG. 3include right and left ends and spaced-apart fingers that are offset, astraight-line configuration similar to third and fourth transverseplates 32 and 34 may also be applied if appropriate.

Referring to FIGS. 2, 3 and 5, the system formed in accordance with thepresent invention also includes left sacral plate 116 and right sacralplate 118. In the illustrated embodiment, sacral plates 116 and 118 areillustrated as being triangulated, however, it should be understood thatit is not necessary to include triangulated sacral plates and straightsacral plates including only two screws, rather than three could beused. In FIGS. 2 and 3, right sacral plate 116 and left sacral plate 118are illustrated. Right sacral plate 118 is a mirror image of left sacralplate 116; therefore, only right sacral plate 118 will be described indetail. Right sacral plate 118 has a base 120 having a posterior surface122 and an opposing anterior surface 124. Anterior surface 124 of sacralplate 118 is designed to intimately contact the posterior surface of thesacrum adjacent the lumbosacral joint. In position, base 120 lies in aplane generally tangential to the portion of the sacrum adjacent to thelumbosacral joint. For purposes of this description, that plane will bereferred to as the sacral or dorsal plane. Base 120 of sacrai plate 118cames three bores that extend from the posterior surface of base 120 ina generally anterior direction. These bores are the pedicle bore 126,the lateral bore 128, and the oblique bore 130. The bores 126, 128, and130, while extending in an anterior direction, are not orthogonal to thesacral plane.

Instead, the pedicle bore 126 has an axis extending in an anterior andmedial direction that is offset in the medial direction preferably at anangle of about 15° to a line orthogonal to the sacrai plane, althoughthis angle may vary depending upon the particular sacral anatomy beingfixed. It is understood that a screw that extends through this boreextends through the pedicle of the sacrum and must always lie within thepedicle.

Lateral bore 128 extends in an anterior and lateral direction that ispreferably offset in the lateral direction at an angle of about 30° froma line orthogonal to the sacral plane. If desired, the lateral angie maybe varied and the direction of the bore canted in either an inferior orsuperior direction relative to the sacral plane depending on the sacralanatomy.

Oblique bore 130 passes through base 120 and is offset in the lateraland inferior directions. Bore 130 when viewed in the sacral plane isfirst preferably offset about 45° from a lateral line, but may be varieddepending on the particular sacral anatomy. The bore 130 is also offsetin the lateral direction preferably about 30° from a line orthogonal tothe sacral plane, but again, may be varied depending upon the particularsacral anatomy.

Extending from the left lateral side of right sacral plate 118 is flange132. Flange 132 is substantially rectangular and has a thickness in theposterior to anterior direction substantially equal to the thickness ofbase 120 in the same direction. Flange 132 extends laterally from base120, in a posterior direction from right to left at an angle of about45° in the illustrated embodiment. Flange 132 is relatively short withrespect to the length of the spaced-apart fingers described below. Thisangle can be varied depending on the particular sacral anatomy.Extending from the end of flange 132 opposite sacral plate 118 aresubstantially parallel spaced-apart fingers 134 of substantially equallength. Ends of spaced-apart fingers 134 opposite flange 132 areconnected by transverse end member 136. Spaced-apart fingers 134 and endmember 136 have a thickness measured in the posterior to anteriordirection approximately equal to one-half the thickness of flange 132 orbody 120 measured in the same direction. This reduced thickness isprovided by removing a portion of the posterior surface 138 ofspaced-apart fingers 134 and end member 136. Posterior surface 138 ofspaced-apart fingers 134 and end member 136 is also textured with arepetitive pattern in a manner similar to first, second, third, andfourth transverse plates described above. As with the transverse plates,flange 132, end member 136 and spaced-apart fingers 138 define a slot140 through right sacral plate 118.

Continuing to refer to FIGS. 2, 3 and 5, left sacral plate 116 includesa base 142 and flange 144 that are substantially minor images of base120 and flange 132 of right sacral plate 118. Extending from flange 144are substantially parallel spaced-apart fingers 146 whose ends oppositeflange 144 are connected by transverse end member 148. Spaced-apartfingers 146, end member 148 and flange 144 define slot 150 through leftsacral plate 116. As with the spaced-apart fingers 134 and the endmember 136 of right sacral plate 118, spaced-apart fingers 146 and endmember 148 of left sacral plate 116 have a thickness measured in theposterior to anterior direction that is approximately equal to one-halfthe thickness of flange 144 or base 142 measured in the same direction.Spaced-apart fingers 146 and end member 148 of left sacral plate 116include an anterior surface 124 that has a portion cut away to providethis thickness. Anterior surface 124 is also textured as describedabove.

Referring to FIGS. 1, 2 and 3, the illustrated system includeslongitudinal plate 42 that includes two spaced-apart elongate members154 whose inferior end and superior end are connected by transversemembers 156 and 158. Transverse end members 156 and 158, andspaced-apart members 154 define a slot 160 through longitudinal plate46. Longitudinal plate 46 is concave in the posterior direction whichprovides the curvature needed to successfully treat spondylolisthesis.The plate is bent on the table to the alignment desired as determined bya template bent to match the patient or the final alignment desired.Longitudinal plate 46 is long enough to extend between first transverseplate 22 and second transverse plate 24 on vertebrae L4 and sacralplates 116 and 118 on the sacram. Longitudinal plate 46 has a thicknessmeasured in the anterior to posterior direction that is substantialenough to provide the rigidity needed for complete fixation andtreatment of the spine.

Referring to primarily FIGS. 2, 3, 4 and 5, fasteners 48, 50 and 52 usedto secure the transverse plates and the sacral plates to thelongitudinal plate are identical except for the differences noted below.Fasteners 48, 50 and 52 include carriage bolt 164, that includes head166, square flange 168 and threaded portion 170. Flange 168 is locatedbetween head 166 and threaded portion 170 and has a thickness that issubstantially equal to the combined thickness of the spaced-apartfingers of the first and second transverse plates, or any of the otherpairs of plates. Flange 168 has a square cross section orthogonal to theaxis of the threaded portion. The lengths of the sides of flange 168 areslightly less than the width of the slots in the transverse plates orsacral plates. Accordingly, a square flange can be positioned within therespective slots and prevented from rotating. Threaded portion 170 isgenerally long enough to extend through the combined spaced-apartfingers of the respective pairs of plates, the other elements of thefastener described below in more detail, and the posterior surface ofthe longitudinal plate. Depending on the particular spinal anatomy,fastener 50 may include a threaded portion that is longer than thethreaded portions for fasteners 48 and 52. Fasteners 48, 50 and 52 alsoinclude a thin primary nut 172 that is threaded to mate with threadedportion 170 on carriage bolt 164. Primary nut 172 includes a posteriorand anterior surface, both of which are textured to facilitate securetightening against the posterior surface of the transverse plates and toprevent slippage between nut 172 and the anterior surface of washer 174described below. After threaded portion 170 is passed through the slotsin a pair of plates, primary nut 172 and carriage bolt 164 are used tosecure spaced-apart fingers of the respective pairs of plates together.Fasteners 48, 50 and 52 also include thin washer 174 that has a bore forreceiving threaded portion 162 of carriage bolt 164 after primary nut172 has been seated. Around periphery, of washer 174 are two flanges 176extending in the posterior direction. Flanges 176 are spaced-apart 180°around the periphery, of washer 174. The lateral distance betweenflanges 176 is large enough so spaced-apart members 154 of thelongitudinal plate 46 will fit between flanges 176. Flanges 176 extendfrom washer 174 in a posterior direction, a distance that is less thanthe thickness of the longitudinal plate measured in the same directionso that the ends of flanges 176 do not extend above longitudinal plate46 when the system is secured together. Alter threaded portion 162 ispassed through slot 160 in longitudinal plate 56, threaded portion 170is secured by secondary, nut 178 that includes a threaded bore formating with threaded portion 170.

Referring to FIGS. 2, 3 and 4, pedicle screws 30, 31, 40, and 41 used tosecure first, second, third and fourth transverse plates to vertebrae L4and L5 include at a lower end a primary threaded portion 58 and at theopposite end a secondary threaded portion 60. Intermediate thesethreaded portions is a flange 184 having a diameter slightly larger thanthe diameter of secondary threaded portion 60. Flange 184 terminates atits upper end in a shoulder that is positioned in a plane orthogonal tothe axis of the screw. The pedicle screws can be secured into vertebraeL4 or L5 down to flange 184 after which the bore in the transverse plateis passed over the secondary threaded end 60 down to the shoulder offlange 184. The bore is sized just slightly larger than the secondarythreaded portion so that the pedicle screw can reciprocate relative toand transverse to the plate, but cannot angulate relative to the screwaxis when engaging the bore. A nut 62 is then threaded onto secondarythreaded portion 60 and used to tighten the anterior surface of theplate against the shoulder of flange 184. A pedicle screw that can beused in the context of the present invention is available from DanekGroup, Inc., Medical Division. To facilitate insertion of the pediclescrew into the pedicle, the end of the pedicle screw adjacent secondarythreaded portion 60 includes an indentation for receiving a tool, suchas an Allen wrench.

Referring to FIGS. 3 and 5, screws 186 used to affix sacral plates 116and 118 to the sacrum include a lower threaded portion 188, an upperflared head 190 and a cylindrical section 192 immediately below head190. Head 190 also carries an Allen socket so that the screw can berotated into a hole drilled in the pedicle. The bone engaging threads onthe lower threaded portion 188 are of conventional design. Cylindricalsection 192 has a diameter slightly less than the diameter of thepedicle bore passing through the sacral plates. The diameters are chosensuch that when cylindrical section 192 is in the bore, the screw canrotate and reciprocate. However, the tolerances are such that the screwcannot angulate or toggle relative to the axis of the bore. Upper flaredhead 190 is configured to mate with a countersink provided in the borewhen the screw is completely threaded into the sacrum. The same screw isemployed in both the lateral bore and the oblique bore.

In use, the system described above can be secured to the lower lumbarregion of the spine in accordance with the following steps. It should beunderstood that differing procedures may be applicable for particularsituations and spinal anatomies.

Referring to FIGS. 2 and 3, pedicle screws 30, 31, 40 and 41 areinserted into the pericles of vertebrae L4 and L5 using conventionaltechniques. Sacral plates 116 and 118 are secured to a sacrum adjacentthe lumbosacral junction with the screws described above. Firsttransverse plate 22 and second transverse 24 plate am loosely matedtogether by passing threaded portion 170 of carriage bolt 164 throughthe slots in first plate 22 and second plate 24. The carriage bolt isloosely held in place threading thin nut 174 on exposed threaded portion170. Bore 78 of second transverse plate 24 is slipped over secondarythreaded portion 60 of right pedicle screw 31 and loosely securedthereto with a conventional nut. Bore 54 of first transverse plate 22 isthen slipped over secondary threaded end 60 of left pedicle screw 30 andsecured loosely thereto with conventional nut 62. Third and fourthtransverse plates 32 and 34 are loosely secured to pedicle screws 40 and41 that have been inserted to vertebrae L5 in a manner similar to thatdescribed above with respect to first transverse plate 22 and secondtransverse plate 24.

With respect to sacral plates 116 and 118, threaded portion 170 ofcarriage bolt 164 is passed through slots 140 and 160 before the sacralplates are secured to the sacrum. Again, a textured nut 172 is used toloosely secure carriage bolt 164 within slots 140 and 160 of left sacralplate 116 and right sacral plate 118. Sacral plates 116 and 118 are thensecured to the sacrum using screws 186. Once the transverse plates andsacral plates are secured to the respective spinal anatomy, texturednuts 172 on carriage bolts 164 can be tightened so that the texturedsurfaces of the respective spaced-apart fingers come in contact andprevent slippage between the respective plates. Next, ranged washer 174is slipped over the exposed end of each of the carriage bolts 164followed by placement of longitudinal plate over the exposed ends of thecarriage bolts. Longitudinal plate is then secured to the sacral platesand the transverse plates using the secondary nuts 178 and the exposedportions of the carriage bolts.

Depending on the degree of displacement and curvature resulting fromspondylolisthesis, initially the anterior side of longitudinal plate 116may not contact washer 174 of the fastener for L5. In order to achievereduction, this gap can be closed by tightening secondary nut 178 oncarriage bolt 164. This tightening causes the system to pull onvertebrae L5 and L4 in a posterior direction while pushing on the sacrumin the anterior direction.

In applying the system described above, it should be understood thatwhile the specific transverse plates are designed to avoid variousanatomical elements of the lower region of the spine, it may benecessary to remove various anatomical elements in order to achieveplacement of the system components. Alternatively, different degrees ofoffset between the bores for the pedicle screws and the spaced-apartfingers can be used.

In accordance with the present invention, pedicle screws are insertedinto the pedicles of vertebrae L4 and L5 so that the pedicle screws areat angles that diverge from each other in the posterior direction. Whenlongitudinal plate is affixed to carriage bolts as described above,before reduction, the distance between the diverging rays associatedwith the pedicle screws would be fixed, e.g., distance A. Afterreduction, when vertebrae L4 and L5 are brought into closer proximitywith longitudinal bar the distance between the diverging rays associatedwith the pedicle screws would be reduced to a distance B, which would beless than A. The system formed in accordance with the present inventionprovides a means for adjusting for this change in distance between thepedicle screws, which allows one to maintain an optimum plate placementwith respect to the plates and the pedicle screws. As the reduction isimplemented, the fasteners can be loosened by loosening nut 178 and nut172. In this manner, the spacing between the individual plates making upthe pairs of plates can be adjusted by allowing the textured surfaces toslide over each other. After the desired spacing is achieved, the nuts172 and 178 can be tightened again to secure the plates together.

While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A transverse platesystem for use in the treatment of spondylolisthesis, comprising:a pairof transverse plates, each of said plates including an eye for receivinga bone screw along a first axis; two spaced-apart substantially parallelfingers extending in a direction transverse to said first axis, saidfingers including a posterior surface and an opposing anterior surface,and said fingers further defining a slot therebetween; and saidposterior surface of said fingers of a first one of said transverseplates, and said anterior surface of said fingers or a second one ofsaid transverse plates each being textured with a repetitive pattern toprevent slippage between said posterior surface and said anteriorsurface when said pair of transverse plates are in contact; said systemfurther including a longitudinal member configured to extend along thelength of the spine; and a fastener for extending between said slot ofeach of said transverse plates when said plates are in contact, andhaving means for engaging said transverse plates to said longitudinalmember.
 2. The transverse plate system of claim 1, wherein each of saidtransverse plates includes an end member extending transversely betweenends of said spaced-apart fingers opposite said eye.
 3. The transverseplate system of claim 1, wherein a longitudinal centerline runs parallelto and between said spaced apart fingers of each of said transverseplates, andfurther wherein said eye is offset from said longitudinalcenterline such that said longitudinal centerline does not intersectsaid first axis.
 4. A sacral transverse plate system comprising:a pairof sacral plates, each having a substantially planar body with aposterior surface and an opposing anterior surface, said anteriorsurface being configured to be positioned against the posterior surfaceof a sacrum adjacent the lumbo-sacral junction, said planar body furtherdefining a number of bores for receiving bone screws there through toengage each of said sacral plates to the sacrum at a location lateralfrom the sagittal plane; a pair of spaced-apart fingers integral withsaid planar body of each of said sacral plates, each of saidspaced-apart fingers including a posterior surface and an opposinganterior surface mid defining a slot therethrough; said posteriorsurface of said fingers of a first one of said sacral plates, and saidanterior surface of said fingers or a second one of said sacral plateseach being textured with a repetitive pattern to prevent slippagebetween said posterior surface and said anterior surface when said pairof sacral plates are in contact; a longitudinal member configured toextend along the length of the spine; and a fastener for extendingbetween said slot of each of said sacral plates when said plates are incontact, and having means for engaging said sacral plates to saidlongitudinal member.